#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    start_index = (k * (k - 1) / 2) + 1
    start_num = (start_index * 2) - 1
    sum = 0
    i = 0
    while i < k:
        sum += start_num
        start_num += 2
        i += 1
    return sum
    

if __name__ == "__main__":
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer